The goal of this project is to study the mechanism of chemically induced murine hepatomas, and to identify and characterize endogenous and exogenous factors that may control initiation, promotion and progression of these tumors. Topics of present interest are: (1) isolation and characterization of preneoplastic liver cell populations; (2) the time course of chemically induced hepatoma formation, and the changes in gene expression during this process; (3) modulating effects of blood flow and oxygen tension on hepatoma formation and development; and (4) the role of genetic predisposition in hepatoma development. Results obtained so far include: (1) centrifugal elutriation method for isolation of different populations (based on size) of parenchymal liver cells from untreated and carcinogen treated rats has been established; (2) computer-assisted analysis of total cellular proteins measured by quantitative two-dimensional gel electrophoresis, in preneoplastic rat hepatocytes as compared to normal hepatocytes, revealed few (5-8) qualitative protein differences. In contrast 10-15% of the cellular proteins in the preneoplastic cells were undergoing quantitative changes of at least 50% during the initiation stage; (3) an early event in hepatocarcinogenesis is a significant reduction of surface receptors for asialoglycoproteins. Based on this observation a new separation method for normal and preneoplastic rat hepatocytes was developed by using asialofetuin as a ligand to selectively bind normal hepatocytes; (4) the anterior chamber of rat eye has been successfully used to grow both normal and preneoplastic rat hepatocytes; (5) a lack of heme induced feedback inhibition of delta-amino-levulenic acid synthetase activity in preneoplastic rat hepatocytes was demonstrated in vitro; and (6) histochemical changes in rat liver following portacaval shunt operation were similar to those observed after administration of hepatocarcinogens, namely increased expression of gamma-glutamyltranspeptidase activity and lack of glucose-6-phosphatase activity. The long-term effects of this operation are under study.